Nature of Operations and Significant Accounting Policies - Unearned Revenue Liability (Details) - Benefits and Protection - Life Insurance - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Nature of Operations and Significant Accounting Policies
Unearned Revenue Liability	$ 475.4	$ 467.4		$ 384.4
Universal life
Nature of Operations and Significant Accounting Policies
Unearned Revenue Liability	$ 466.6	$ 459.0	$ 425.3	384.4
Previously reported
Nature of Operations and Significant Accounting Policies
Unearned Revenue Liability				335.6
Previously reported | Universal life
Nature of Operations and Significant Accounting Policies
Unearned Revenue Liability				335.6
Adjustment for reversal of unrealized gain (loss) from AOCI | ASU 2018-12 - Targeted improvements to the accounting for long-duration insurance contracts
Nature of Operations and Significant Accounting Policies
Unearned Revenue Liability				48.8
Adjustment for reversal of unrealized gain (loss) from AOCI | ASU 2018-12 - Targeted improvements to the accounting for long-duration insurance contracts | Universal life
Nature of Operations and Significant Accounting Policies
Unearned Revenue Liability				$ 48.8